unscheduled offworld activation (idea)

An unscheduled offworld activation is a Stargate-related event on the television shows Stargate SG-1 and Stargate Atlantis. When humanity rediscovered the Stargate and began sending teams through it to other planets on a regular basis, it was decided that a mechanism was needed to block the Stargate on Earth when it was not in use to prevent the Goa'uld or any of Earth's other enemies from walking into Stargate Command anytime they pleased. A special iris was created and installed on Earth's Stargate that prevents anyone or anything from being able to arrive through Earth's gate as long as the iris is closed; anyone that arrives at the closed Stargate gets their molecules splattered across the iris instantly. Teams that are sent to other planets ("offworld") as part of Earth's Stargate program are given small devices that transmit identifiable access codes back to Stargate Command to tell the base to open the iris and allow the teams to return. Teams arrive and depart on a set schedule, and the iris is commonly left open just prior to a scheduled arrival through the Stargate on Earth. However, when somebody offworld activates the Earth Stargate when there are no scheduled arrivals expected, the iris is immediately closed, warning klaxons are sounded, and various warning lights flash. This reaction is known as an unscheduled offworld activation.

Unscheduled offworld activations (UOA) are treated with extreme seriousness at Stargate Command on Stargate SG-1. After all, a UOA is analagous to someone knocking at your front door and if you're not expecting somebody to visit you want to be sure that your door is locked. Radio and video signals can still be transmitted through the closed iris, so it's standard procedure at Stargate Command to try and communicate with whomever has activated the Stargate unexpectedly. Sometimes it's just an SG Team coming home early, other times there's a stranger at the other end of the Stargate who is curious about what "this big stone ring" does, and other times it's an Earth-friendly planet calling to share information. Most times a UOA signals an attempted enemy attack or invasion, however, so it's understandable why Stargate Command takes an incoming Stargate wormhole so seriously. There are a small handful of species that can activate a Stargate without needing to dial it first (such as the Asgard and the Nox, for example), and these sudden Stargate activations are always treated as an UOA for security purposes even though species that have this ability are peaceful and Earth-friendly. At the lost ancient city of Atlantis in the Pegasus Galaxy on Stargate Atlantis UOA are somewhat rare since the city has been lost for so long that very few people know where it is or what symbols make up its Stargate address. Since that information is lost, Atlantis receives very few UOAs, but as the humans who have discovered the city begin to move around the Pegasus Galaxy and make friends and enemies it is likely that UOAs will become a routine event there as well.